The present invention relates to piston compressors, and in particular to cooling arrangements for such compressors.
The invention concerns a multi-stage piston compressor with a compressor unit having a plurality of air-cooled cylinders. The compressor crankshaft is housed in a crankcase and is driven by a motor unit that is flange-mounted on an end face on said compressor unit. On the opposing end face of the compressor unit is arranged a cooler unit, mounted on said compressor unit and driven by the crankshaft. An integrated axial fan wheel of said cooler unit blows cooling air substantially outward along the compressor unit. Moreover, the invention also concerns a rail vehicle with a compressed air system, especially a pneumatic brake system, which comprises such a multi-stage piston compressor for generating compressed air.
The area of application of the invention extends primarily to rail vehicle design. Rising environmental requirements in regard to pollution emission and noise protection are leading increasingly to the use of oil-free piston compressors in noise-encapsulated designs. Compressors for rail vehicles which run in residential regions or are parked there and held in readiness require an ever increasing expense on noise optimization of their equipment. With compressors in noise protection capsules, on the other hand, the problem of an adequate cooling of the compressor unit arises, because soundproofing materials generally also have good thermal insulation properties. Yet cooling problems do not occur only in such noise protection capsules, but also with installations in machine rooms or outdoor installations in the vicinity of heat sources, such as air conditioning units.
German patent documents no. DE 10 2010 024 346 A1 discloses a single-stage compressor unit in which the cooling air is generated by a radial fan, which is secured at the drive side of the compressor unit between the latter and the motor unit. In this technical solution, the cooling air is moved in the compressor's transverse direction and at the same time distributed among all cylinders. This requires a corresponding expense on components for the largely nested cooling air guidance.
Furthermore, single-stage or multi-stage piston compressors are also known from the general prior art in which the cooling air is blown from an axial fan directly onto the cylinders of the compressor unit. In order to prevent the cooling air from flowing off radially, a force guidance of the axially directed air flow is generated along the cylinders. Even so, a large portion of the cooling air of the axial fan is lost due to swirling caused by collisions with the cylinders.
Therefore, the problem which the present invention proposes to solve is to create an external cooling air guidance especially for a multi-stage piston compressor, which enables an efficient cooling of the cylinders of the compressor unit with slight expense on components.
The invention includes the technical teaching that, for the conducting of cooling air externally in the region of said compressor unit at least one air guide housing which extends at least partially radially around the crankcase in a curved manner is mounted on said cooler unit on the air inlet side and is mounted on the compressor unit crankcase on the air outlet side, such that the axially directed air flow which is generated by said axial fan wheel is at least partially taken in by the air guide housing and at least partially guided around the crankcase in the radial direction so as to reach at least one cylinder of the compressor unit arranged on the air outlet side of said air guide housing.
In other words, the external cooling air guidance according to the invention takes in the cooling air generated by the axial fan and deflects it by preferably around 90° from the axial direction to a radial direction about the crankcase, so that it then flows out against a cylinder of the compressor unit. Thus, the external cooling air guidance according to the invention directly adjoins the cooler unit and passes on the air flow generated by the axial fan wheel. Due to the curvature of the arc-shaped air guide housing, the air flow is deflected into a laminar flow for the efficient cooling of an air-cooled cylinder of the compressor unit which is outfitted with cooling ribs. Preferably, the cylinder arranged at the air outlet side of the air guide housing is matched up with a high-pressure stage of the preferably multi-stage compressor unit. Because of this the high-pressure stage of a multi-stage compressor unit is generally under greater thermal load than the upstream low-pressure stage. Furthermore, the high-pressure stage on account of the higher pressure is more temperature-sensitive in terms of wear on the component parts. Therefore, an efficient cooling of the high-pressure stage is especially important, and this is provided for by the solution according to the invention. An inadequate cooling, on the other hand, may lead to an intensified wear on component parts and thus a shorter service life or a premature compressor breakdown.
The improved cooling furthermore allows the piston compressor of the invention to be installed in so-called noise protection capsules, which provides a box-shaped receptacle for the piston compressor and its built-on parts and is lined with a soundproofing material. In this way, the noise output of the piston compressor is reduced and at the same time the temperatures at the compressor unit as well as the gas outlet temperatures are increased little if at all, or even lowered as compared to a non-encapsulated arrangement, thanks to the external cooling air guidance according to the invention. In addition, the invention is equally suited to installation at hot spots in a vehicle where the supply of cold cooling air is deficient, or generally for operation in hot climate zones of the Earth.
Preferably the air guide housing can extend in the radial direction around the crankcase of the compressor unit by a deflection angle of 90° to 360°. In one preferred embodiment, the air guide housing extends around the crankcase by around 90°. The compressor unit in this case is in a boxer design (i.e., having horizontally-opposed cylinders disposed on opposite sides of the crankshaft) and two air baffles are provided, being arranged opposite each other on the crankcase, each of them being matched up with one cylinder for the cooling. According to one preferred embodiment, the compressor unit comprises a total of three cylinders, two cylinders being matched up with a low-pressure stage and the remaining cylinder with a high-pressure stage. The cylinder of the high-pressure stage is preferably arranged next to the cooler unit, looking in the axial direction.
However, the cooling air guidance can also include the neighboring cylinder of the low-pressure stage and likewise cool it. The air guide housing is configured so that the cooling air flow moves around the entire fin position of the cylinder. Especially important in this case is the flow around the external cooling fins, i.e., the cooling fins close to the cylinder head. Of course, the cooling air guidance can also be used for the cooling of cylinders of single-stage compressors.
According to one measure which improves the invention it is proposed to arrange at least one fin for deflecting the cooling air in the radial direction at the inside of the wall of the air guide housing, extending radially in the direction of the crankcase. According to one preferred embodiment, two opposing fins which are spaced apart are arranged in the region of the cylinder being cooled on the air guide housing. The respective distal end of the fins can bear against the crankcase and thus define the distance between crankcase and air guide housing. The fins which are curved in the flow direction preferably lie vertically in the region of the upper and lower boundary of the cylinder being cooled according to the preferred embodiment. The fins take up the cooling air flow directed downward at a slant and deflect it horizontally toward the cylinder. Furthermore, the fins generate a back pressure in front of the cylinder being cooled, which increases the flow velocity in the region of the cooling fins of the cylinder, boosting the efficiency.
According to one preferred embodiment, the air guide housing at the air inlet side is configured such that it takes up the cooling air from the cooler unit through a radial region of 120° to 220°, preferably 180°. If two mutually opposing air guide housings are arranged on the crankcase in the context of a preferred embodiment—as described above—an uptake will occur preferably through a radial region of 180°. In this case, contact protection means are no longer necessary to cover the fan wheel, since it is entirely enclosed by the two air guide housings. Otherwise, appropriate contact protection means must be put in place in the areas of the cooler unit not contact-protected by the air guide housing.
According to one preferred embodiment of the air guide housing, the latter is a sheet metal design. The arc-shaped housing can be produced by rounding or edging the sheets. The air guide housing needs to be cut out in places requiring elastic mounting elements for the fastening of the piston compressor. According to one preferred embodiment, the air guide housing is multiple-piece, individual housing pieces being detachably joined together by a plug connection or by a screw connection. This improves the installation, accessibility, and servicing for purposes of cleaning the cooling fins.
However, it is also conceivable to have a single-piece air guide housing, preferably one made from injection-molded plastic. In this case, the fins serving for the air guidance can be easily molded on in the manufacturing process. Alternatively, the air guide housing can be cast at least partly from a light metal or the like.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.